1. Field of the Invention
The invention relates to a power converter. In particular, the invention relates to a phase adjustment circuit of a power converter, the power converter, and a control method of the power converter.
2. Description of Related Art
FIG. 1 is a schematic diagram illustrating a conventional power converter. FIG. 2 is a schematic diagram illustrating waveforms in a conventional power converter. Please refer to both FIG. 1 and FIG. 2. The existing power converter 100 is often designed in a circuit structure featuring a constant on time (COT) control architecture. A comparator 110 of the power converter 100 generates a comparison signal Xcm by comparing an error signal Xerr with a ramp signal Xramp. A timing controller circuit 120 generates a pulse width modulation (PWM) signal Xpwm according to the comparison signal Xcm, an input voltage Vin, and an output voltage Vout. Here, the width of the on time Ton of the PWM signal Xpwm is fixed in each cycle, and the width of the on time Ton (as shown in FIG. 2) is associated with the input voltage Vin and the output voltage Vout.
In the power converter 100, the comparison signal Xcm is generated according to the error signal Xerr and the ramp signal Xramp, and the time point at which the on time Ton of the PWM signal Xpwm is output is determined according to the comparison signal Xcm. The value of the error signal Xerr is associated with both a feedback signal Vfb and a reference voltage Vref. When it is determined to output the on time Ton of the PWM signal Xpwm, the timing controller circuit 120 starts to calculate to obtain the on time Ton, and the on time Ton of the PWM signal Xpwm is fixed in each cycle.
The conventional PWM operation may ensure the fixed frequency. However, if an equivalent serial resistance DCR of an inductor L and an equivalent serial resistance ESR of a capacitor CL at an output terminal of the power converter 100 are rather small, the energy compensated by the capacitor CL and the inductor L in response to the transient variation of the load is delayed, and therefore the feedback signal Vfb and the error signal Xerr are also delayed. The error signal Xerr originally generated by a compensation circuit 130 can no longer be applied to converge the output voltage Vout, and hence the waveforms of the output voltage Vout oscillate in a noticeable manner.